1. Field of the Invention
The present invention relates generally to ventilation of crawlspaces beneath buildings and more specifically to foundation vents for installation in the foundation of a building to provide crawlspace ventilation.
2. Background of the Invention
Ventilation of the crawlspace beneath a building is imperative to prevent moisture build-up and consequent moisture damage to floor joist, rim joists, decking, and other structural elements exposed to the crawlspace. Ventilation also helps to prevent the build-up within the crawlspace of potentially harmful or explosive gasses such as methane, natural gas, ozone, and sewer gas. A variety of methods of providing crawlspace ventilation have been used over the years. Many early homes, fore example, were simply built upon brick pilings so that the crawl space was open around the periphery of the house. Obviously, no ancillary ventilation is required in this type of building construction. In more recent years, homes have been built upon raised foundation walls, which are visually more appealing than open foundations but that also create a closed crawlspace beneath the home that must be ventilated. Early attempts to provide crawlspace ventilation generally were very crude and usually involved leaving open ventilation holes at selected locations around the foundation. While such ventilation holes do provide ventilation, they nevertheless are problematic because, among other things, they provide an opening through which insects and vermin can enter the crawlspace. Further, holes in the foundation provide no means of regulating the amount of ventilation, which is important in cold weather to conserve heat and prevent freezing of sub-structural plumbing.
In more modern times, foundation vents have been developed. Foundation vents are designed to be built into the foundation walls of a home or other building to provide reliable and regulatable crawlspace ventilation. While foundation vents are available in a wide variety of designs, in general they include a frame that is securable within an opening in a foundation wall. Typically, the frame is rectangular in shape and is conveniently sized to fit within the space normally occupied by a cinder block of the foundation wall. The frame surrounds and supports a grill structure, which allows air flow through the vent but deters entry into the crawlspace of mice, squirrels, chipmunks, and other small vermin. In order to prevent entry into the crawlspace of relatively smaller insects such as roaches and bees, most foundation vents also are provided with a mesh screen mounted to the back side of the grill. Finally, an adjustable air flow regulator is provided for selective restriction of the amount of air that flows through the vent. Air flow regulators can take a variety of forms in foundation vents, but two of the most common are a sliding shudder mechanism and an inwardly hinging damper that can be opened and closed by a handle. In either case, the foundation vent can be fully or partially opened or completely closed as desired.
Early foundation vents generally were fabricated from metal with their frames and grills, for example, being made of cast aluminum and with components such as damper panels being made of stamped sheet aluminum. With the advent of improved weather resistant plastics, however, many foundation vents today, especially in residential construction, are made of injection molded plastic. Nevertheless, the design and function of plastic foundation vents is substantially the same as that of their metal predecessors.
An important functional consideration when designing foundation vents is the "net free area" of the vent. Net free area refers to the total amount of open or free area provided for the flow or air through the vent. For example, a rectangular opening in a foundation wall with no foundation vent installed has a net free area equal to the product of the length and width of the opening. When a foundation vent is installed, however, the frame, grill structures, and screen of the vent cover and block some of the opening, thus reducing the net free area available for the flow or air. In fact, it is not unusual for a foundation vent to have a net free area that is half or even less that of the opening in which it is installed.
Foundation vents with smaller net free areas impose the requirement on builders that more vents be installed to accomplish a given total air flow through a crawlspace. The required installation of more vents is undesirable because of the extra cost of vents and, more importantly, the additional time and labor costs associated with installing more vents. Thus, designers of foundation vents strive to maximize the net free area of their vents by optimizing the frame and grill structures of the vents. However, there are inherent limits to the amount that net free area can be increased because of constraints imposed by structural requirements and the requirement that a vent's grill openings be small enough to prevent vermin from entering through the vent. Accordingly, the frame and grill structures of modern foundation vents generally are already optimized to provide the maximum possible net free area allowed by design constraints.
To make matters worse, the mesh screens mounted to the back surfaces of the grill of a foundation vent covering the grill openings reduces net free area even further. In modern plastic foundation vents, the screens generally are secured by being sonically welded or hot staked to the back of the grill and around the rim of the frame. While the individual aluminum or fiberglass strands of the screen appear small to the eye, their combined area can, in fact, block a significant portion of the grill openings and reduce the net free area of the vent by up to twenty percent (20%). Unfortunately, the mesh screen can not be eliminated because it is required to prevent entry of insects into the crawlspace.
Clearly, there exists a need for a foundation vent that meets all of the pre-imposed requirements of structural integrity and pest impenetrability while at the same time presenting a net free area to the flow of air that is substantially increased over that presented by existing prior art foundation vents. Such a foundation vent also should be economical to produce, easy to install, selectively openable and closable as needed, and, due to its increased net free area, reduce the required number of vents that a contractor must install to obtain a total required crawlspace airflow. It is to the provision of such a foundation vent that the present invention is primarily directed.